1. Field of the Invention
The present invention is broadly concerned with novel anionic substantially biodegradable and substantially water soluble polymers and derivatives thereof which have significant utility in agricultural applications, especially plant nutrition and related areas. More particularly, the invention is concerned with such polymers, as well as methods of synthesis and use thereof, wherein the preferred polymers have significant levels of anionic groups. Additionally, the preferred polymers also include significant levels of alcohol groups. The most preferred polymers of the instant invention include recurring polymeric subunits made up of vinylic (e.g., vinyl acetate or vinyl alcohol) and dicarboxylic (e.g., maleic acid, itaconic acid, anhydrides, and other derivatives thereof) moieties. The polymers may be complexed onto ions and/or mixed with or coated with phosphate-based fertilizers to provide improved plant nutrition products.
2. Description of the Prior Art
Lignosulfonates, polyacrylates, polyaspartates and related compounds have become known to the art of agriculture as materials that facilitate nutrient absorption. All of them suffer from significant disadvantages, which decrease their utility in comparison to the art discussed herein and limit performance.
Lignosulfonates are a byproduct of paper pulping; they are derived from highly variable sources. They are subject to large, unpredictable variations in color, physical properties, and performance in application areas of interest for this invention.
Polyacrylates and polymers containing appreciable levels thereof can be prepared with good control over their composition and performance. They are stable to pH variations. However, polyacrylates have just one carboxylate per repeat unit and they suffer from a very significant limitation in use, namely that they are not biodegradable. As a result, their utility for addressing the problems remedied by the instant invention is low.
Polyaspartates are biodegradable, but are very expensive, and are not stable outside a relatively small pH range of about 7 to about 10. They usually have very high color, and incorporate amide groups, which causes difficulties in formulating them. Additionally, polyaspartates have just one carboxylate per repeat unit and are therefore not a part of the present invention.
Russian Journal of Applied Chemistry, 24(5):485-489 (1951) teaches the preparation of maleic anhydride-vinyl acetate copolymers in benzene and acetone with benzoyl peroxide initiators. It further discloses the addition of above copolymers to water, wherein the polymer gradually self-hydrolyzes to a complex mixture containing units of maleic acid, vinyl alcohol, vinyl acetate, lactones, free acetic acid, and other species. Deficiencies of this teaching include undesirable presence of lactone, which decreases number of dicarboxylic groups. In addition, no use for polymers is taught or suggested.
U.S. Pat. Nos. 3,268,491 and 3,887,480 teach preparation of maleic acid-vinyl acetate copolymers in water-based solutions using redox-based initiators in a certain pH range. The approaches described in these patents are highly problematic. Only redox-type initiators are claimed to be useful. A fixed pH range restricts the practice. Only a narrow range of copolymers composed exclusively from the monomers of maleic acid and vinyl acetate are taught. The process of U.S. Pat. No. 3,268,491 is deemed to be non-commercial by U.S. Pat. No. 3,887,480 which described improved processes but uses over 17% by weight of redox initiator; such processes are very wasteful, have high environmental impact, and are not cost effective.
U.S. Pat. Nos. 5,191,048 and 5,264,510 teach copolymerization of acrylic acid, maleic acid, and vinyl acetate with subsequent hydrolysis by base. Again, several important deficiencies are evident. Among these are the exclusive use of base hydrolysis and preferred embodiments of invention incorporating monocarboxylic acids. Only terpolymers are disclosed. Furthermore, the intended uses of the compositions are very restricted and in no way teach, suggest or imply utility of the enumerated and contemplated compositions for the purposes of the present invention.
It will thus be seen that the prior art fails to disclose or provide polymers which can be synthesized using a variety of monomers and techniques in order to yield end products which are substantially biodegradable, substantially water soluble, and have wide applicability for agricultural uses.
The present invention overcomes the problems outlined above and provides a new class of anionic polymers having a variety of uses, e.g., for enhancing takeup of nutrient by plants or for mixture with conventional phosphate-based fertilizers to provide an improved fertilizer product. Advantageously, the polymers are biodegradable, in that they degrade to environmentally innocuous compounds within a relatively short time (up to about 1 year) after being in intimate contact with soil. That is to say that the degradation products are compounds such as CO2 and H2O or the degradation products are absorbed as food or nutrients by soil microorganisms and plants. Similarly, derivatives of the polymers and/or salts of the polymers (e.g. ammonium salt forms of the polymer) also degrade within a relatively short time, during which significant fractions of the weight of the polymer are believed to be metabolized by soil organisms.
Broadly speaking, the anionic polymers of the invention include recurring polymeric subunits made up of at least two different moieties individually and respectively taken from the group consisting of what have been denominated for ease of reference as A, B and C moieties. Thus, exemplary polymeric subunits may be AB, BA, AC, CA, ABC, BAC, CAB, or any other combination of A moieties with B and C moieties. Moreover, in a given polymer different polymeric subunits may include different types or forms of moieties, e.g., in an AB recurring polymeric unit polymer, the B moiety may be different in different units.
In detail, moiety A is of the general formula 
moiety B is of the general formula 
and moiety C is of the general formula 
wherein R1, R2 and R7 are individually and respectively selected from the group consisting of H, OH, C1-C30 straight, branched chain and cyclic alkyl or aryl groups, C1-C30 straight, branched chain and cyclic alkyl or aryl C1-C30 based ester groups (formate (C0), acetate (C1), propionate (C2), butyrate (C3), etc. up to C30), Rxe2x80x2CO2 groups, and ORxe2x80x2 groups, wherein Rxe2x80x2 is selected from the group consisting of C1-C30 straight, branched chain and cyclic alkyl or aryl groups; R3 and R4 are individually and respectively selected from the group consisting of H, C1-C30 straight, branched chain and cyclic alkyl or aryl groups; R5, R6, R10 and R11 are individually and respectively selected from the group consisting of H, the alkali metals, NH4 and the C1-C4 alkyl ammonium groups, Y is selected from the group consisting of Fe, Mn, Mg, Zn, Cu, Ni, V, Cr, Si, B, Co, Mo, and Ca; R8 and R9 are individually and respectively selected from the group consisting of nothing (i.e., the groups are non-existent), CH2, C2H4, and C3H6, at least one of said R1, R2, R3 and R4 is OH where said polymeric subunits are made up of A and B moieties, at least one of said R1, R2 and R7 is OH where said polymeric subunits are made up of A and C moieties, and at least one of said R1, R2, R3, R4 and R7 is OH where said polymeric subunits are made up of A, B and C moieties.
As can be appreciated, the polymers of the invention can have different sequences of recurring polymeric subunits as defined above (for example, a polymer comprising A, B and C subunits may include the one form of A moiety, all three forms of B moiety and all three forms of C moiety). In the case of the polymer made up of A and B moieties, R1-R4 are respectively and individually selected from the group consisting of H, OH and C1,-C4 straight and branched chain alkyl groups, R5 and R6 are individually and respectively selected from the group consisting of the alkali metals.
The most preferred polymers of the invention are made up of recurring polymeric subunits formed of A and B moieties, wherein R5 and R6 are individually and respectively selected from the group consisting of H, Na. K, and NH4 and specifically wherein R1, R3and R4 are each H, R2 is OH, and R5 and R6 are individually and respectively selected from the group consisting of H, Na, K, and NH4 depending upon the specific application desired for the polymer. These preferred polymers have the generalized formula 
wherein R5 and R6 are individually and respectively selected from the group consisting of H, the alkali metals, NH4 and C1-C4 alkyl ammonium groups (and most preferably, H, Na, K and NH4 depending upon the application), and n ranges from about 1-10000 and more preferably from about 1-5000.
For purposes of the present invention, it is preferred to use dicarboxylic acids, precursors and derivatives thereof for the practice of the invention. For example, terpolymers containing mono and dicarboxylic acids with vinyl esters and vinyl alcohol are contemplated, however, polymers incorporating dicarboxylic acids were unexpectedly found to be significantly more useful for the purposes of this invention. This finding was in contrast to the conventional teachings that mixtures of mono and dicarboxylates were superior in applications previously suggested for mono-carboxylate polymers. Thus, the use of dicarboxylic acid derived polymers for agricultural applications is unprecedented and produced unexpected results. It is understood that when dicarboxylic acids are mentioned herein, various precursors and derivatives of such are contemplated and well within the scope of the present invention. Put another way, copolymers of the present invention are made up of monomers bearing at least two carboxylic groups or precursors and/or derivatives thereof. The polymers of the invention may have a wide variety of molecular weights, ranging for example from 500-5,000,000, more preferably from about 1,500-20,000, depending chiefly upon the desired end use.
In many applications, and especially for agricultural uses, the polymers of the invention may be mixed with or complexed with a metal or non-metal ion, and especially ions selected from the group consisting of Fe, Mn, Mg, Zn, Cu, Ni, Co, Mo, V, Cr, Si, B, and Ca. Alternatively, polymers containing, mixed with or complexed with such elements may be formulated using a wide variety of methods that are well known in the art of fertilizer formation. Examples of such alternative methods include, forming an aqueous solution containing molybdate and the sodium salt of polymers in accordance with the invention, forming an aqueous solution which contains a zinc complex of polymers in accordance with the present invention and sodium molybdate, and combinations of such methods. In these examples, the presence of the polymer in soil adjacent growing plants would be expected to enhance the availability of these elements to these growing plants. In the case of Si and B, the element would merely be mixed with the polymer rather than having a coordinate metal complex formation. However, in these cases, the availability of these ions would be increased for uptake by growing plants and will be termed xe2x80x9ccomplexedxe2x80x9d for purposes of this application.
The polymers hereof (with or without complexed ions) maybe used directly as plant growth enhancers. For example, such polymers may be dispersed in a liquid aqueous medium and applied foliarly to plant leaves or applied to the earth adjacent growing plants. It has been found that the polymers increase the plant""s uptake of both polymer-borne metal nutrients and ambient non-polymer nutrients found in adjacent soil. In such uses, plant growth-enhancing amounts of compositions comprising the above-defined polymers are employed, either in liquid dispersions or in dried, granular form. Thus, application of polymer alone results in improved plant growth characteristics, presumably by increasing the availability of naturally occurring ambient nutrients. Typically, the polymers are applied at a level of from about 0.001 to about 100 lbs. polymer per acre of growing plants, and more preferably from about 0.005 to about 50 lbs. polymer per acre, and still more preferably from about 0.01 to about 2 lbs.
In other preferred uses, the polymers may be used to form composite products where the polymers are in intimate contact with fertilizer products including but not limited to phosphate-based fertilizers such as monoammonium phosphate (MAP), diammonium phosphate (DAP), any one of a number of well known N-P-K fertilizer products, and/or fertilizers containing nitrogen materials such as ammonia (anhydrous or aqueous), ammonium nitrate, ammonium sulfate, urea, ammonium phosphates, sodium nitrate, calcium nitrate, potassium nitrate, nitrate of soda, urea formaldehyde, metal (e.g. zinc, iron) ammonium phosphates; phosphorous materials such as calcium phosphates (normal phosphate and super phosphate), ammonium phosphate, ammoniated super phosphate, phosphoric acid, superphosphoric acid, basic slag, rock phosphate, colloidal phosphate, bone phosphate; potassium materials such as potassium chloride, potassium sulfate, potassium nitrate, potassium phosphate, potassium hydroxide, potassium carbonate; calcium materials, such as calcium sulfate, calcium carbonate, calcium nitrate; magnesium materials, such as magnesium carbonate, magnesium oxide, magnesium sulfate, magnesium hydroxide; sulfur materials such as ammonium sulfate, sulfates of other fertilizers discussed herein, ammonium thiosulfate, elemental sulfur (either alone or included with or coated on other fertilizers); micronutrients such as Zn, Mn, Cu, Fe, and other micronutrients discussed herein; oxides, sulfates, chlorides, and chelates of such micronutrients (e.g., zinc oxide, zinc sulfate and zinc chloride); such chelates sequestered onto other carriers such as EDTA; boron materials such as boric acid, sodium borate or calcium borate; and molybdenum materials such as sodium molybdate. As known in the art, these fertilizer products can exist as dry powders/granules or as water solutions.
In such contexts, the polymers may be co-ground with the fertilizer products, applied as a surface coating to the fertilizer products, or otherwise thoroughly mixed with the fertilizer products. Preferably, in such combined fertilizer/polymer compositions, the fertilizer is in the form of particles having an average diameter of from about powder size (less than 0.001 cm) to about 10 cm, more preferably from about 0.1 cm to about 2 cm, and still more preferably from about 0.15 cm to about 0.3 cm. The polymer is present in such combined products at a level of from about 0.001 g to about 20 g polymer per 100 g phosphate-based fertilizer, more preferably from about 0.1 g to about 10 g polymer per 100 g phosphate-based fertilizer, and still more preferably from about 0.5 g to about 2 g polymer per 100 g phosphate-based fertilizer. Again, the polymeric fraction of such combined products may include the polymers defined above, or such polymers complexed with the aforementioned ions. In the case of the combined fertilizer/polymer products, the combined product is applied at a level so that the polymer fraction is applied at a level of from about 0.001 to about 20 lbs. polymer per acre of growing plants, more preferably from about 0.01 to about 10 lbs polymer per acre of growing plants, and still more preferably from about 0.5 to about 2 lbs polymer per acre of growing plants. The combined products can likewise be applied as liquid dispersions or as dry granulated products, at the discretion of the user. When polymers in accordance with the present invention are used as a coating, the polymer comprises at least about 0.01% by weight of the coated fertilizer product, more preferably the polymer comprises at least about 5% by weight of the coated fertilizer product, and most preferably comprises at least about 10% by weight of the coated fertilizer product.
Additionally, use of polymers in accordance with the present invention increases the availability of phosphorus and other common fertilizer ingredients and decreases nitrogen volatilization, thereby rendering ambient levels of such plant nutrient available for uptake by growing plants. In such cases, the polymer can be applied as a coating to fertilizer products prior to their introduction into the soil. In turn, plants grown in soil containing such polymers exhibit enhanced growth characteristics.
Another alternative use of polymers in accordance with the present invention includes using the polymer as a seed coating. In such cases, the polymer comprises at least about 0.01% by weight of the coated seed, and more preferably comprises at least about 5% by weight of the coated seed, and still more preferably comprises at least about 10% by weight of the coated seed.
In general, the polymers of the invention are made by free radical polymerization serving to convert selected monomers into the desired polymers with recurring polymeric subunits. Such polymers may be further modified to impart particular structures and/or properties. A variety of techniques can be used for generating free radicals, such as addition of peroxides, hydroperoxides, azo initiators, percarbonate, per-acid, charge transfer complexes, irradiation (e.g., UV, electron beam, X-ray, gamma-radiation and other ionizing radiation types), and combinations of these techniques. Of course, an extensive variety of methods and techniques are well known in the art of polymer chemistry for initiating free-radical polymerizations. Those enumerated herein are but some of the more frequently used methods and techniques. Any suitable technique for performing free-radical polymerization is likely to be useful for the purposes of practicing the present invention
The polymerization reactions are carried out in a compatible solvent system, namely a system which does not unduly interfere with the desired polymerization, using essentially any desired monomer concentrations. A number of suitable aqueous or non-aqueous solvent systems can be employed, such as ketones, alcohols, esters, ethers, aromatic solvents, water and mixtures thereof. Water alone and the lower (C1-C4) ketones and alcohols are especially preferred, and these may be mixed with water if desired. In most instances, the polymerization reactions are carried out with the substantial exclusion of oxygen, and most usually under an inert gas such as nitrogen or argon. There is no particular criticality in the type of equipment used in the synthesis of the polymers, i.e., stirred tank reactors, continuous stirred tank reactors, plug flow reactors, tube reactors and any combination of the foregoing arranged in series may be employed. A wide range of suitable reaction arrangements are well known to the art of polymerization.
In general, the initial polymerization step is carried out at a temperature of from about 0xc2x0 C. to about 120xc2x0 C. (more preferably from about 30xc2x0 C. to about 95xc2x0 C. for a period of from about 0.25 hours to about 24 hours and even more preferably from about 0.25 hours to about 5 hours. Usually, the reaction is carried out with continuous stirring.
After the initial polymerization, the products are recovered and hydrolyzed so as to replace at least certain of the ester-containing groups on the polymer with alcohol groups, thereby providing the polymers defined previously. Generally, the hydrolyzing step involves the addition of an acid or base to the polymerized product in the presence of water. Polymers comprising monomers with vinyl ester groups (polymers formed at least in part from A moieties) need to have sufficient base added to neutralize all of the carboxylic acid groups and form a substantial number of alcohol groups from the precursor vinyl ester groups. Thereafter, the completed polymer may be recovered as a liquid dispersion or dried to a solid form. It is important to note that both acid and base hydrolysis are useful in practicing the present invention so that under appropriate conditions, sufficient acid must be added in order to form a substantial number of alcohol groups. Additionally, in many cases it is preferred to react the hydrolyzed polymer with an ion such as Fe, Mn, Mg, Zn, Cu, Ni, Co, Mo, V, Cr, and Ca to form a coordinate metal complex. Techniques for making metal-containing polymer compounds are well known to those skilled in the art. In some of these techniques, a metal""s oxide, hydroxide, carbonate, salt, or other similar compound may be reacted with the polymer in acid form. These techniques also include reacting a finely divided free metal with a solution of an acid form of a polymer described or suggested herein. Additionally, the structures of complexes or salts of polymers with metals in general, and transition metals in particular, can be highly variable and difficult to precisely define. Thus, the depictions used herein are for illustrative purposes only and it is contemplated that desired metals or mixtures of such are bonded to the polymer backbone by chemical bonds. Alternatively, the metal may be bonded to other atoms in addition to those shown. For example, in the case of the structure shown herein for the second reactant, there may be additional atoms or functional groups bonded to the Y. These atoms include, but are not limited to, oxygen, sulfur, halogens, etc. and potential functional groups include (but are not limited to) sulfate, hydroxide, etc. It is understood by those skilled in the art of coordination compound chemistry that a broad range of structures may be formed depending upon the preparation protocol, the identity of the metal, the metal""s oxidation state, the starting materials, etc. Alternatively, acid hydrolysis may be performed followed by a reaction to form a complex with a previously enumerated metal. In yet another alternative method, the polymer may be isolated and subsequently formulated in such a way that the hydrolysis reaction occurs in situ, in the soil or during mixture with a fertilizing composition. In this alternative method, unhydrolyzed polymer is added to soil or fertilizer compositions of appropriately low or high pH such that when contacted by water, a microenvironment of low or high pH is produced. It is within this microenvironment that hydrolysis occurs and alcohol groups are formed. In the case of Si and B ions, the polymer is merely mixed with these ions and does not form a coordinate complex. However, the availability of these ions to growing plants is increased.
In more detail, the preferred method for polymer synthesis comprises the steps of providing a reaction mixture comprising at least two different reactants selected from the group consisting of first, second, and third reactants. The first reactant is of the general formula 
the second reactant is of the general formula 
and the third reactant is of the general formula 
With reference to the above formulae, R1, R2 and R7 are individually and respectively selected from the group consisting of H, OH, C1-C30 straight, branched chain and cyclic alkyl or aryl groups, C1-C30 straight, branched chain and cyclic alkyl or aryl C1-C30 based ester groups (formate (C0), acetate (C1), propionate (C2), butyrate (C3), etc. up to C30), Rxe2x80x2CO2 groups, and ORxe2x80x2 groups, wherein Rxe2x80x2 is selected from the group consisting of C1-C30 straight, branched chain and cyclic alkyl or aryl groups; R3 and R4 are individually and respectively selected from the group consisting of H, C1-C30 straight, branched chain and cyclic alkyl or aryl groups; R5, R6, R10 and R11 are individually and respectively selected from the group consisting of H, the alkali metals, NH4 and the C1-C4 alkyl ammonium groups, Y is selected from the group consisting of Fe, Mn, Mg, Zn, Cu, Ni, Co, Mo, V, Cr, Si, B, and Ca; R8 and R9 are individually and respectively selected from the group consisting of nothing (i.e., the groups are non-existent), CH2, C2H4, and C3H6, at least one of said R1, R2, R3 and R4 is OH where said polymeric subunits are made up of A and B moieties, at least one of said R1, R2 and R7 is OH where said polymeric subunits are made up of A and C moieties, and at least one of said R1, R2, R3, R4 and R7 is OH where said polymeric subunits are made up of A, B and C moieties.
Selected monomers and reactants are dispersed in a suitable solvent system and placed in a reactor. The polymerization reaction is then carried out to obtain an initial polymerized product having the described recurring polymeric subunits. Thereupon, the initial polymer product is hydrolyzed to the alcohol form. Put another away, the general reaction proceeds by dissolving monomers (e.g., maleic anhydride and vinyl acetate) in a solvent (e.g., acetone). The amount of monomers incorporated can be either equimolar or non-equimolar. A free radical initiator is then introduced and copolymerization takes place in solution. After the reaction is complete and substantially all monomer has been reacted, the resulting solution is a maleic anhydride-vinyl acetate copolymer. Of course, if all monomers have not undergone polymerization, the resulting solution will contain a small portion of monomers which do not affect later use of the polymer. The solution is concentrated and subjected to hydrolysis (either in situ or by performing a hydrolysis reaction during manufacture) with a sufficient amount of base (e.g., NaOH) in the presence of water. This base neutralizes a substantial majority of the carboxylic acid groups and converts a substantial majority of the polymer""s acetate groups into alcohol groups. The anhydride groups are converted to carboxylic acid sodium salt groups arranged in groups of two on the backbone of the polymer. The resulting copolymer is then isolated by conventional methods such as precipitation.
Again, it is important to note that the aforementioned methods and procedures are merely preferred methods of practicing the present invention and those skilled in the art understand that a large number of variations and broadly analogous procedures can be carried out using the teachings contained herein. For example, acid hydrolysis can also be used followed optionally by formation of various derivatives or the hydrolysis may be carried out naturally in soil under sufficient moisture and pH conditions. The acid hydrolysis isolates the polymers of the present invention in a substantially acid form which renders them highly versatile and useful. These polymers may be used as is (in the acid form) or further reacted with various materials to make salts and/or complexes. Furthermore, complexes or salts with various metals may be formed by reacting the acid form with various oxides, hydroxides, carbonates, and free metals under suitable conditions. Such reactions are well known in the art and include (but are not limited to) various techniques of reagent mixing, monomer and/or solvent feed, etc. One possible technique would be gradual or stepwise addition of an initiator to a reaction in progress. Other potential techniques include the addition of chain transfer agents, free radical initiator activators, molecular weight moderators/control agents, use of multiple initiators, initiator quenchers, inhibitors, etc. Of course, this list is not comprehensive but merely serves to demonstrate that there are a wide variety of techniques available to those skilled in the art and that all such techniques are embraced by the present invention.
Another alternative method involves taking an aqueous solution of, for example, caustic and stirring it in a suitable container. Next, an acetone reaction mixture containing, for example, acetone and a copolymer of maleic anhydride with vinyl acetate is added to the caustic solution. Throughout this addition, the polymer going into the caustic solution will experience a high pH and have the acetate groups hydrolyzed to the alcohol form. In acid-base titrations such as this, at the point where one reagent is just exhausted, a very sharp pH change usually takes place with minimal addition of the second reagent. Therefore, in this reaction, just enough acetone-polymer reaction solution is added to bring the apparent pH of the now final polymer product-acetone-water mixture to about 7. At this time, the mixture is subjected to reduced pressure distillation to remove acetone. The result is an aqueous solution at a neutral pH that contains the desired polymer. From this solution, it may be isolated by a variety of ways, including but not limited to precipitation, spray drying, simple drying, and etc. The only side effect of a reaction of this type is that a small fraction of the polymer is going to contain acetate groups which are not hydrolyzed to alcohol.
The foregoing description is useful in instances where polymers in accordance with the present invention, upon dissolution in water, give a solution that is alkaline. In many cases, this alkalinity is not a problem as the solution pH can be adjusted to neutral or acidic with a suitable mineral or organic acid. However, the formulation of this powder into some liquid formulations containing metals is problematic. High-pH solutions of metal salts tend to form insoluble metal hydroxides that precipitate and/or exhibit other behaviors that are undesirable from the point of view of formulation ease and convenience, as well as nutrient availability. One way to remedy this problem, other than as described in the preceding paragraph, is to add a mineral or organic acid to the aqueous solution of polymer salt in order to bring the pH close to neutral.
The following examples set forth techniques for the synthesis of polymers in accordance with the invention, and various uses thereof. It is to be understood that these examples are provided by way of illustration only and nothing therein should be taken as a limitation upon the overall scope of the invention.